Underground vaults have been used for storing and/or housing various items or equipment. One such use is for the housing of electrical and optical elements of communication systems. Such an application is described in U.S. Pat. No. 4,776,138, and is incorporated by reference herein.
Most commonly, vaults for this purpose are made by concrete walls and floors. In the past, construction of underground vaults has been performed by either casting the floors and walls in-place with concrete or by prefabricating the concrete elements and assembling them beneath the ground. However, neither of these approaches has been totally satisfactory. A concrete cast-in-place structure has been manufactured something in the form similar to that of a storm shelter. The ordinary construction has been a skeleton of reinforcing bars or wire mesh inside of concrete walls. Cast-in-place concrete vaults can be undesirable because of the amount of time and man-hours it takes to install due to their size, amount of concrete required, and concrete setting requirements. A typical cast-in-place concrete vault has internal dimensions upwards of 32′ length by perhaps 10′ width and a ceiling height of 9′. The wall thickness is relatively thick to assure a substantial structure, the gross weight is approximately 90 tons or more. Handling and transporting a 90 ton structure is somewhat difficult. Often, such concrete vaults have been fabricated in sections for easier transport. Concrete vaults, however, made from prefabricated sections and assembled below ground can be undesirable because the wall thickness of such panels must be relatively thick to ensure a substantial structure. Thus, the concrete panels are typically very heavy and the handling and transporting of the panels of such weight can be burdensome. The joints of assembled in place concrete vaults are leak prone due to ground water hydrostatic pressure. Also, this approach requires that the equipment that is housed in the concrete vault be integrated on the work site during the assembly process. This causes the equipment to be exposed to the outdoor environment. Long on site assembly time is undesirable due to lost operational time of the house equipment. Particularly, when telecommunication equipment is used to provide commercial services, delays in making the equipment operational reduces the revenues and increases overhead costs for the service provider.
U.S. Pat. No. 4,776,138 to Simmer et al. discloses a vault made primarily from fiberglass. However, this vault design also has drawbacks. For example, such a vault requires a different mold design for each vault which makes customization expensive and impractical. Further, fabrication may be difficult or time consuming in that the sheets must be individually wrapped around the mold. This assembly is then covered with a balsa-wood or foam. After that step, additional fiberglass is applied.